phranque - 3:49 am on May 17, 2013 (gmt 0)
this applies specifically to the USA but has general suggestions that apply elsewhere and echos much of what swa66 suggested.
CAN-SPAM Act: A Compliance Guide for Business | BCP Business Center:
if you follow the bulk email best practices and guidelines suggested by the major email providers you should be in good shape.
Mail Help | - SLN3435 - Best practices for bulk mail senders and postmasters when sending to Yahoo! Mail:
[Microsoft] Policies, Practices, and Guidelines:
Bulk Senders Guidelines - Gmail Help: